target/arm: Implement FEAT_E0PD

target/arm: Implement FEAT_E0PD

FEAT_E0PD adds new bits E0PD0 and E0PD1 to TCR_EL1, which allow the
OS to forbid EL0 access to half of the address space.  Since this is
an EL0-specific variation on the existing TCR_ELx.{EPD0,EPD1}, we can
implement it entirely in aa64_va_parameters().

This requires moving the existing regime_is_user() to internals.h
so that the code in helper.c can get at it.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20221021160131.3531787-1-peter.maydell@linaro.org